The present invention relates generally to growth containers such as petri dishes. More specifically, the present invention relates to a petri dish having a two-position lid which provides, alternatively, means to permit or prevent gas exchange between the interior of the petri dish and the atmosphere.
The concept of employing what is known as petri dishes for growing bacteria colonies is well known. Petri dishes are often constructed of glass and usually define a circular lower portion which has an upstanding annular wall adapted to contain a material such as agar or gelatin as a culture medium for the bacteria. The lower portion is covered with a similarly shaped cover having a slightly larger diameter so that it encompasses the lower portion. The petri dish has been defined as a small shallow dish of thin glass, with a loosely fitting overlapping cover, used for plate cultures in bacteriology.
Of more recent vintage are the petri dishes constructed of plastic material and, therefore, so inexpensively fabricated that they may be disposed after a single use, thereby eliminating the relatively expensive washing and sterilization process ordinarily required. A plastic type petri dish may be fabricated at the factory and may then have included therein the agar, all under sterile conditions. They can be individually packaged for use in a biological laboratory.
Two types of petri dishes are known, namely, those the covers of which have projections on their inner surfaces and those the covers of which are free of projections on the inner surfaces. Those with projections usually have three small, about 1 to 2 min. high, nub-like projections that lie on the flat edge of the lower dish to prevent the cover from lying closely upon the edge of the lower dish so that a slit is formed through which gas exchange is possible with the inner space of the petri dish. After pouring in a nutrient substrate, especially a gel-like nutrient substrate such as agar, gas exchange is important for the culturing process. In the case of anaerobic culture processes, gas exchange may be important for the removal of oxygen or of the oxygen-containing atmosphere, or for the replacement thereof.
Although the structure of a petri dish is quite simple, it must perform its intended function as efficiently and inexpensively as possible. Ideally, the petri dish should be a shallow rigid container which is easily manipulable by a technician with respect to manual placement and removal of the cover. Also, the petri dish should efficiently receive and distribute liquid nutrient media during the manufacturing process so that a uniform layer of solidified media with a continuous meniscus with the side wall of the bottom container is obtained. In this regard, the interior configuration of the bottom container should not impede the distribution of the liquid nutrient media during filling.
Petri dishes are commonly, but not exclusively, used to culture prokaryotic (i.e., viruses, bacteria and bacteriophage) and eukaryotic (i.e., tissue culture, plant sales, molds, fungi, yeast, microscopic worms and many eggs and embryos) cells or organisms. These cells are grown in a liquid medium or on a solid medium which supplies the needed nutrients to the cells. Other uses include sample storage such as field sample collection, food testing and laboratory experiments.
When dishes are filled with a solid medium they are often stored for days or months before use. Most hospitals and medical clinics buy prefilled dishes which can be as old as six months. Many scientific laboratories have technicians who pour dishes for the entire lab, or the researchers pour their own dishes. In either case, more dishes are poured than are usually needed at the time for convenience. However, the solid medium will dry out if the dishes are not kept in a sealed package or individually wrapped, since the lids are typically designed to allow free gas exchange. After the dishes have been used they can be discarded, but sometimes in laboratory research they are kept and the colonies are used to start new cultures at another time. Again, the petri dishes must be wrapped to prevent dehydration. This can be very tiresome if there are a large number of dishes to be wrapped.
Accordingly, there has been a need for an improved petri dish which can be manufactured inexpensively, maintains all of the principal advantages of prior petri dishes, and yet incorporates features which significantly improve the utility thereof. Such an improved petri dish should preferably permit the technician to grow cultures therein selectively under aerobic or anaerobic conditions, utilizing the same basic components. Further, an improved petri dish is needed which is easily sealed, without wrapping, after filling with a nutrient medium and which, by a mere change in component configuration, may be utilized to grow tissue cultures therein while permitting gas exchange to occur. Moreover, a novel petri dish incorporating the above features should be stable when stacked one atop another and permit parallel or perpendicular stacking arrangements. The present invention fulfills these needs and provides other related advantages.